The present invention is related to liquid cooling of dynamoelectric machines and more particularly to rotor cooling in dynamoelectric machines.
High speed, high power density switched reluctance motors have a significant portion of the overall electromagnetic losses occur in the magnetic rotor laminations. Removal of these losses is done through liquid coolants which are guided through the shaft on which the rotor laminations are mounted. As the fluid cannot readily be brought into direct contact with the laminations, the heat has to be carried through the laminations to the shaft and then into the fluid. Effective heat transfer requires a large transfer area and high fluid velocity, the combination of which is difficult to achieve in the confines of the shaft. Present implementations result in significant heat input into the bearings and excessive heating of the lamination assembly, limiting the total power conversion capability of the machine because of the bearing and lamination assembly temperature restrictions.
High power density motors have been cooled using water cooled stators and/or heat pipes embedded in the rotor. Some large generators have been cooled with several circuits of water cooling passing through hollow rotor bars. In the case of rotor heat pipes, the removal of heat from the heat pipe condensing sections using forced air flow, still causes a major thermal resistance. While the water circuits in large rotors are very effective for rotor cooling, they would either excessively interfere with rotor performance in small motors or would be very costly and unreliable if made small enough to not interfere with motor performance.
It is an object of the present invention to provide a dynamoelectric machine with more effective heat transfer to a liquid in a cooled rotor.
It is a further object of the present invention to provide a dynamoelectric machine with increased heat transfer coefficients over the heat transfer surfaces in a liquid cooled rotor without the need for small coolant passages (microchannels) employing large coolant flow rates.
It is another object of the present invention to provide improved heat transfer to cooling fluids in a rotor in a relatively limited space for improved power density of the dynamoelectric machine.
It is a still further object of the present invention to provide a dynamoelectric machine not requiring high coolant flow rates and complex coolant passageways difficult to manufacture and operate reliably.